Strikes indicate ‘huge battle’ may be on way that will be a key test of Kyiv troops’ ability to push Russia back

• Russia-Ukraine war: latest updates

The war in Ukraine may be heading for its bloodiest phase yet, according to senior Ukrainian officials and western analysts, who say a long-threatened southern counteroffensive by Kyiv’s forces will result in a “huge battle” and will need to overcome increasingly well dug-in Russian troops.

People interviewed by the Guardian, including those who have recently escaped Kherson, describe Russian forces in the south building hardened tank shelters, digging trenches and bringing in prefabricated concrete pillboxes by lorry.

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The United States estimates that Russian casualties in Ukraine so far have reached around 15,000 killed and perhaps 45,000 wounded, CIA director William Burns said.

“The latest estimates from the US intelligence community would be something in the vicinity of 15,000 (Russian forces) killed and maybe three times that wounded. So a quite significant set of losses,” Burns said while speaking at the Aspen Security Forum in Colorado.

Russia is prioritising the capture of critical national infrastructure, such as power plants.

However, it is probably also attempting to break through at Vuhlehirska, as part of its efforts to regain momentum on the southern pincer of its advance towards the key cities of Kramatorsk and Sloviansk.”